So, I recently watched a video regarding the first synthesized fertilizer, and I thought it was pretty interesting that farmland was basically screwed if they didn’t figure out how to get more nitrogen into dirt.
But then I thought about it, I was taught that plants make the bulk of themselves out of carbon, which they absorb from the air in carbon dioxide. Why is the same not true with nitrogen? Our atmosphere is a little more than 2/3rds nitrogen after all.
I tried looking it up, but the result was basically “Because nitrogen in the atmosphere is in a gaseous form” but that wasn’t really helpful.
In: 91
Was it from “Veritasium”? If so he explains In the video I think how nitrogen in our atmosphere is diatomic. nitrogen and plants can’t absorb this type of nitrogen easily it first needs to be split into single atoms of nitrogen. this process takes energy and with nitrogen it’s an extreme amount of energy. Plants depend on microbes and mycelium in the soil to break this nitrogen down into a usable mono form look up nitrogen fixation on “Journey to the microcosmos” to learn more
N2 nitrogen in the air is not useful to plants, it needs to first be “fixed” (converted to usable organic forms). Bacteria in the soil do this and so plants have evolved to just obtain their nitrogen from the soil. They could have probably evolved to do it themselves but there was no need as bacteria already did it.
This only becomes a problem when you want to pack more plants into a smaller section of soil and bacteria cant provide enough nitrogen. For the crop yields we get today we need fertilizers to make up for what the soil bacteria cant do.
The core of the issue is that it take a lot of energy to convert N2 (atmospheric nitrogen) into Nitrate (NO3^- ), and is difficult for a plant or animal to do in their cells.
To illustrate the energy intensity of the process, AFAIK, the main mechanism for N2 to get converted to NO3^- is lightning strikes.
The nitrogen-nitrogen triple bond is one of the Most stabile Bonds
Which translates to nitrogen beeing very unreactive, its Just difficult to turn it into anything but its diatonic Form, that it is in in air
Nitrogen in the air is like a product packed in way too sturdy plastic ([you probably know what I mean](https://en.wikipedia.org/wiki/File:Wrap_Rage_Example.jpg)). It’s technically there, but you can’t use it without a tool. Some bacteria have scissors. They can open the packaging and make it useful – to them, and also to others afterwards.
Nitrogen usually forms three bonds. As gas, all three bonds are formed with another nitrogen atom. That’s a very sturdy connection that is difficult to break apart. Plants don’t have the tools for that. Some bacteria do, and they use the nitrogen to make other molecules where the nitrogen is bound to three different atoms. That’s much more accessible, now you only need to break one bond at a time. Fertilizer has nitrogen in more accessible form, too.
Oxygen and CO2 are much easier to break apart.
The process you are talking about is called nitrogen fixation. It is done by the nitrogenase enzyme. Plants do not have this enzyme but live in symbiose with bacteria living on the roots and in the soil which does the nitrogen fixation. So there is normally no need for plants to do this themselves.
The problem is that nitrogen fixation takes a lot of energy. Unlike carbon dioxide the dinitrogen in the air require much more energy to break the bonds. So nitrogen fixating bacteria consume a lot of energy, much more then the leaf cells on a plant generate from the sun. These bacteria get their energy mostly from sugars released by the plants through their roots. When the plants lack nitrogen compounds they release their sugar straight into the soil and the nitrogen fixating bacteria use this sugar to make amonia and other nitrogen fertilizers. Nematodes and amoeba will then eat the bacteria and release any excess nitrogen compounds which the plants then absorb through their roots.
However by making nitrogen fertilizers from energy rich natural gas or electricity we are essentially doing the bacterias jobs for them. By adding this nitrogen to the soil the plants are never low on nitrogen and therefore does not release sugar into the soil and the nitrogen fixating bacteria dies out. This of course means that the plants are able to use the sugars themselves to grow faster and larger.
Nitrogen atoms really, *really* like to be stuck to one other Nitrogen atom. So much so that it is very difficult to get atmospheric nitrogen (which is 2 nitrogen atoms stuck together) to do anything else, like form an amino acid.
Some plants pull it off by making friends with specific soil bacteria that can break apart Nitrogen-Nitrogen bonds.
Nitrogen in the air is very strong, and cannot be broken by plants.
So this needs to be fixed, or broken down. In nature, lightning has enough energy to do this, breaking nitrogen down. But a lot of man made processes have been invented to do this as well.
It takes a huge amount of energy to break the bonds between the atoms of nitrogen in the atmosphere. The bond is so strong that concentrated nitrate fertilizer is a high explosive. Fertilizer bombs are very real, and [fertilizer factories sometimes explode](https://www.csb.gov/west-fertilizer-explosion-and-fire-/) The city of Lebanon was devastated when a warehouse full of fertilizer exploded. Basically, in order to make nitrogen based fertilizer, energy is pumped into nitrogen, and it is capable of releasing that energy with catastrophic speed. Some plants- mostly in the legume family (beans) can partner with bacteria in their roots, they pay the bacteria energy (sugar) in exchange for nitrate. But it is so expensive, most plants evolved to just use what is present in the environment.
Nitrogen in the air is actually formed as two atoms of Nitrogen “triple bonded” together. This is very strong and hard to break into each individual atom of nitrogen.
Soil bateria use atmospheric Nitrogen to eat and as a result they can break the “triple bond” leaving Nitrogen in other forms which the plant can use.
Latest Answers